In mammals, the digestion of nutrients and the elimination of waste are controlled by the gastrointestinal system. Within this system, there are a number of natural peptides, ligands, enzymes, and receptors which play a vital role and are potential targets for drug discovery. Modifying the production of, or responses to these endogenous substances can have an effect upon the physiological responses such as diarrhea, nausea, and abdominal cramping. One example of an endogenous substance which affects the gastrointestinal system is motilin.
Motilin is a peptide of 22 amino acids which is produced in the gastrointestinal system of a number of species. Although the sequence of the peptide varies from species to species, there are a great deal of similarities. For example, human motilin and porcine motilin are identical; while motilin isolated from the dog and the rabbit differ by five and four amino acids respectively. Motilin induces smooth muscle contractions in the stomach tissue of dogs, rabbits, and humans as well as in the colon of rabbits. Apart from local gastrointestinal intestinal tissues, motilin and its receptors have been found in other areas. For example motilin has been found in circulating plasma, where a rise in the concentration of motilin has been associated with gastric effects which occur during fasting in dogs and humans. Itoh, Z. et al. Scand. J. Gastroenterol. 11:93–110, (1976); Vantrappen, G. et al. Dig. Dis Sci 24, 497–500 (1979). In addition, when motilin was intravenously administered to humans it was found to increase gastric emptying and gut hormone release. Christofides, N. D. et al. Gastroenterology 76:903–907, 1979.
Aside from motilin itself, there are other substances which are agonists of the motilin receptor and which elicit gastrointestinal emptying. One of those agents is the antibiotic erythromycin. Even though erythromycin is a useful drug, a great number of patients are affected by the drug's gastrointestinal side effects. Studies have shown that erythromycin elicits biological responses that are comparable to motilin itself and therefore may be useful in the treatment of diseases such as chronic idiopathic intestinal pseudo-obstruction and gastroparesis. Weber, F. et al., The American Journal of Gastroenterology, 88:4, 485–90 (1993).
Although motilin and erythromycin are agonists of the motilin receptor, there is a need for antagonists of this receptor as well. The nausea, abdominal cramping, and diarrhea which are associated with motilin agonists are unwelcome physiological events. The increased gut motility induced by motilin has been implicated in diseases such as Irritable Bowel Syndrome and esophageal reflux. Therefore researchers have been searching for motilin antagonists.
One such antagonist is OHM-11526. This is a peptide derived from porcine motilin which competes with both motilin and erythromycin for the motilin receptor in a number of species, including rabbits and humans. In addition, this peptide is an antagonist of the contractile smooth muscle response to both erythromycin and motilin in an in vitro rabbit model. Depoortere, I. et al., European Journal of Pharmacology, 286, 241–47, (1995). Although this substance is potent in that model (IC50 1.0 nM) it is a peptide and as such offers little hope as an oral drug since it is susceptible to the enzymes of the digestive tract. Zen Itoh, Motilin, xvi (1990). Therefore it is desirable to find other non-peptidic agents which act as motilin antagonists. The compounds of this invention are such agents.
The compounds of this invention are non-peptidyl motilin antagonists with potencies and activities comparable to known peptidyl motilin antagonists. These compounds compete with motilin and erythromycin for the motilin receptor site in vitro. In addition, these compounds suppress smooth muscle contractions induced by motilin and erythromycin with activities and potencies comparable to OHM 11526 in an in vitro model.